Blasting cap electric firing system



June 23, 1959 A. A. WOLF 2,892,128

BLASTING CAP ELECTRIPC FIRING svsmm Filed June 25. 1954 INVENTOR ATTORNEY United States Patent BLASTING CAP ELECTRIC FIRING SYSTEM Alfred A. Wolf, Dallastown, Pa., assign'or to Fidelity Instrument Corporation, York, Pa., a corporation of Pennsylvania Application June 23, 1954, Serial No. 438,651

Claims. (Cl. 317-80) My invention relates to an improved electric system for firing blasting caps, and particularly to a system in which the inadvertent firing of the blasting caps below a desired predetermined voltage is prevented, and in which the blasting cap firing circuit is disconnected from the source of electric power supply after a substantially predetermined time.

The electric firing system to which this invention pertains is particularly useful for firing a large number of blasting caps, such as a thousand or twelve hundred, and to assure substantially simultaneous firing of all of these caps. The system may be used for a smaller number of caps, and provision is made for preventing damage to the system and injury to operators because the full capacity of the system is not utilized under such conditions. The electric system may be supplied with power from any suitable source of power supply, such as a manually operable and controlled direct current generator of the hand-crank or push-down type conventionally utilized in this type of system. Since manually operable direct current generators of the type conventionally used in blasting systems generate voltages which are dependent upon the speed at which they are operated, it is important that the firing circuit for the blasting caps should not be energized until a suitable voltage has been attained in order to insure that all caps connected to the firing circuit will detonate the explosive charges substantially simultaneously.

In my improved electric firing system for blasting machines, I provide a control system for connecting a source of electric power supply to a firing circuit through an intermediate firing charge condenser. This firing charge condenser is adapted to be initially charged by the source of electric power supply, to be disconnected from the source of electric power supply, and to be connected to a blasting cap firing circuit for a substantially predetermined time in order to detonate the blasting caps, and then to be disconnected from the firing circuit and reconnected to the source of electric power supply so as to be substantially completely discharged. This assures the supply of electrical energy to the firing circuit at the desired voltage, provides for the connection of the firing circuit to the condenser for the desired time, and assures against energization of the firing circuit after the desired detonation.

An object of my invention is to provide an improved electric firing system for a blasting machine.

Another object of my invention is to provide an improved electric firing system for a blasting machine in which a firing circuit is completely deenergized after a predetermined time.

A further object of my invention is to provide an improved electric firing system for a blasting machine in which provision is made for energizing the firing circuit of the system only after a predetermined voltage is availice 2 able and for deenergizing the firing circuit after a predetermined time.

Further objects and advantages of my invention will become apparent from the following description, referring to the accompanying drawing, and the features of novelty which characterizes my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

The single figure in the drawing schematically illustrates a blasting cap electric firing system in accordance with one embodiment of my invention.

Referring to the drawing, I have shown my improved electric firing system for a blasting machine in which the electrical energy for detonating blasting caps is adapted to be supplied by any suitable source of electric power supply, such as a manually operable and controlled direct current generator 1 of any suitable type, such as a conventiona crank-operated or push-down generator. Since the voltage of the generator 1 depends basically upon its speed of operation in conventional machines of this type, it is desirable that the energy from the generator 1 should not be supplied to a firing circuit for the blasting caps until the desired voltage for proper operation has been attained. In order to assure this desired operation, a control system is provided which includes a firing charge condenser 2, which is adapted to be electrically charged by the generator 1 and is electrically connected to one side of the generator 1 by a direct con nection 3 and to the other side of the generator 1 through contacts 4 and 5 of an electromagnetic relay having an energizing winding 6. This relay winding 6 is directly connected at 7 to one side of the generator 1 and the other side thereof is connected to the other side of the generator 1 through a series connected resistor 8 and a manually operable control switch 9. The resistance of the resistor 8 and the resistance and inductance of the relay winding 6 are chosen such that current flowing through the relay winding 6 is insufficient to operate the relay until a predetermined desired voltage is generated by the generator 1, thus making the operation of this relay responsive to the voltage of generator 1. With the winding 6 insufficiently energized to operate the relay, the generator 1 supplies electric energy to the firing charge condenser 2 so as to charge this condenser. The firing charge condenser 2 is adapted to be connected across a firing circuit, including terminals 10 and 11, by being connected thereto through contacts 12 and 13 of an electromagnetic relay having an energizing winding 14. The contacts 12 and 13 of this relay are normally open so as to disconnect the firing charge condenser 2 from the firing circuit.

When the generator 1 is operated, it also supplies electric energy to a second condenser 15 through contacts 16 and 17 of the voltage-responsive relay operable by the winding 6. Thus, both the condenser 2 and the condenser 15 are charged by the generator 1 as it builds up voltage, and when the predetermined desired firing voltage is attained, the manually operable switch 9 being closed, the relay winding 6 will be energized and the relay will pick up, opening the charging circuits which connect both the condenser 2 and the condenser 15 to the generator 1. If desired, the manually operable switch 9 may be left open and when the voltage of generator 1 reaches the predetermined value the switch 9 may be closed. This energizes relay winding 6 and it picks up as desired. When this relay picks up, the contact 5 will close on relay contacts 18 and connect the relay winding 6 directly across the generator 1 through a holding circuit completed by the contacts 5 and 18. This serves to keep the relay winding 6 energized suificiently to hold the relay in its picked up position until the generator 1 has substantially been allowed to come to rest. The circuit between the contacts 16 and 17 of this relay is opened when the relay picks up, and the contact 17 closes a circuit through relay contacts 19 which places the condenser 15 directly across the other relay winding 14, thereby discharging the condenser 15 through the winding 14 and energizing this relay Winding. Energization of the relay winding 14 picks up this relay and closes a circuit through the relay contacts 12 and 13, which places the firing charge condenser 2 across the firing circuit connected to the terminals 10 and 11, thus energizing the firing circuit at the desired predetermined voltage of the condenser 2, which was reached by the generator 1 at the time the condenser 2 was disconnected from the generator 1. The electric characteristics of the relay winding 14, that is, its inductance and resistance, and the electrical characteristic of the condenser 15, that is, its ca pacitance, are made such that the condenser 15 will supply an energization to the winding 14 adequate to hold the relay contacts 12 and 13 closed for a predetermined time, and to open the circuit through the contacts 12 and 13 and assure against further energization of the firing circuit after the predetermined time. This assures against inadvertent detonation of blasting caps and against possible short circuits in the firing circuit, which might occur if the firing circuit remained energized beyond the desired detonating period. When the generator 1 is allowed to come to rest after the blasting caps have been detonated, the relay Winding 6 is deenergized and the holding circuit through the contacts and 18 no longer provides energy to the winding 6 so that the relay again is opened and assumes the position illustrated in the drawing. Under these conditions the firing charge condenser 2 is reconnected directly across the generator 1, such that any electric charge remaining in the condenser 2 will be dissipated through the generator 1, thus assuring complete deenergization of the electric firing system.

While I have illustrated and described a particular embodiment of my invention, modification thereof will occur to those skilled in the art. I desire it to be understood that I intend in the annexed claims to cover all modifications within the spirit and scope of this invention as therein defined.

I claim:

1. A blasting cap electric firing system including a manually operable electric generator providing a source of electric power supply, a firing circuit, a firing charge condenser, and a control system having first electromagnetic means for connecting said firing charge condenser to said firing circuit on energization of said first electromagnetic means, means for energizing said first electromagnetic means for a predetermined time, a holding circuit, other electromagnetic means for normally connecting said firing charge condenser to said source of electric power supply for charging said condenser and for disconnecting said firing charge condenser from said source of electric power supply and for connecting said other electromagnetic means for energization through said holding circuit to said source of electric power supply and connecting said first electromagnetic means to said energizing means.

2. A blasting cap electric firing system including a manually operable source of electric power supply, a firing circuit, a firing charge condenser, and a control system having first electromagnetic means for connecting said firing charge condenser to said firing circuit on energization of said first electromagnetic means, means for energizing said first electromagnetic means for a predetermined time, a holding circuit, other electromagnetic means for normally connecting said firing charge condenser to said source of electric power supply for charging said condenser and operable in response to a predetermined voltage of said source of electric power supply for disconnecting said firing charge condenser from said source of electric power supply and for connecting said other electromagnetic means for energization through said holding circuit to said source of electric power supply and connecting said first electromagnetic means to said energizing means.

3. A blasting cap electric firing system including a manually operable electric generator providing a source of electric power supply, a firing circuit, a firing charge condenser, and a control system having a second condenser, first electromagnetic means for connecting said firing charge condenser to said firing circuit, a holding circuit, other electromagnetic means for normally connecting said firing charge condenser and said second condenser to said source of electric power supply for charging said condensers and on energization in response to a predetermined voltage of said source of electric power supply disconnecting said firing charge condenser and said second condenser from said source of electric power supply and for connecting said other electromag netic means for energization through said holding circuit to said source of electric power supply and connecting said first electromagnetic means for energization by said second condenser, said second condenser and said first electromagnetic means having electrical characteristics for providing for connection of said firing charge condenser to said firing circuit for a substantially predetermined time, said other electromagnetic means being arranged and connected for reconnecting said firing charge condenser to said source of electric supply generator when said generator is not operated providing for discharging said firing charge condenser through said generator.

4. A blasting cap electric firing system comprising a manually operable electric generator for providing a source of electric power, a firing circuit, a firing charge condenser, a firing charge condenser charging circuit having a normally closed first switch device for connecting said condenser across said generator, first electromagnetic means for connecting said firing charge condenser to said firing circuit upon the energization of said first electromagnetic means, a second condenser, a discharge circuit for said second condenser comprising said first electromagnetic means and a second normally open switch device, a charging circuit having a third normally closed switch device for connecting said second condenser across said generator, other electromagnetic means for actuating the aforementioned switches when energized by a selected value of voltage, and circuit means for energizing said other electromagnetic means by said generator to actuate said aforementioned switches to open said firing charge condenser charging circuit, to close said discharge circuit for said second condenser and to open the charging circuit of said second condenser whereby said first electromagnetic means will be energized to connect the firing charge condenser to the firing circuit.

5. A blasting cap electric firing system comprising a manually operable electric generator for providing a source of electric power, a firing circuit, a firing charge condenser, a firing charge condenser charging circuit having a normally closed first switch device for connecting said condenser across said generator, first electromagnetic means for connecting said firing charge condenser to said firing circuit upon the energization of said first electromagnetic means, a second condenser, a discharge circuit for said second condenser comprising said first electromagnetic means and a second normally open switch device, a charging circuit having a third normally closed switch device for connecting said second condenser across said generator, other electromagnetic means for actuating the aforementioned switches when energized by a selected value of voltage, a circuit having a serially connected resistance for energizing said other electromagnetic means by said generator, a fourth normally open switch device actuated by said other electromagnetic means, said fourth switch being in shunting relation to said re- References Cited in the file of this patent UNITED STATES PATENTS Stuart Mar. 9, 1943 Weisg1ass Feb. 26, 1946 Stein Sept. 2, 1952 Mufiiy Dec. 30, 1952 Schmitt June 30, 1953 

